U.S. patent number 4,072,645 [Application Number 05/706,354] was granted by the patent office on 1978-02-07 for transparent pre-cure coating for rubbery polymers.
This patent grant is currently assigned to The Goodyear Tire & Rubber Company. Invention is credited to Richard J. Cogley, Jr..
United States Patent |
4,072,645 |
Cogley, Jr. |
February 7, 1978 |
Transparent pre-cure coating for rubbery polymers
Abstract
Light-colored unvulcanized polymers such as those used in the
white sidewall areas of pneumatic vehicle tires are coated with a
carbon black-free, pre-cure paint comprised of a polymer containing
hydrated amorphous silica and a zinc activation system in a
solubilizable form. The paint may have an aqueous or non-aqueous
base; i.e., vehicle.
Inventors: |
Cogley, Jr.; Richard J. (South
Gate, CA) |
Assignee: |
The Goodyear Tire & Rubber
Company (Akron, OH)
|
Family
ID: |
24837195 |
Appl.
No.: |
05/706,354 |
Filed: |
July 19, 1976 |
Current U.S.
Class: |
524/575 |
Current CPC
Class: |
B05D
7/02 (20130101); C09D 109/08 (20130101) |
Current International
Class: |
B05D
7/02 (20060101); C09D 109/00 (20060101); C09D
109/08 (20060101); C08L 009/10 () |
Field of
Search: |
;260/29.7M,29.7SQ,23.7M |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Welsh; M. J.
Attorney, Agent or Firm: Brunner; F. W. Rozmajzl; J. A.
Claims
What is claimed is:
1. A pre-cure paint comprising:
a. a rubbery diene polymer,
b. hydrated amorphous silica,
c. a zinc salt or zinc complex which is soluble in the rubbery
diene polymer, and
d. a paint vehicle.
2. The paint according to claim 1 wherein the zinc salt or zinc
complex is formed in situ in the rubbery diene polymer from zinc
oxide.
3. The paint of claim 1 wherein contains sulfur.
4. The paint of claim 3 wherein the zinc salt or complex is formed
by a reaction between zinc oxide and a compound selected from the
group consisting of ammonium sulfate, the tetrasodium salt of
ethylene diamine tetra acetic acid, triethylene tetra amine,
tetraethylene pentamine, sodium gluconate and sodium citrate.
5. The paint according to claim 4 wherein the zinc oxide is reacted
with ammonium sulfate.
6. A process of preparing the unvulcanized rubbery surface of a
product prior to vulcanization of the product, said surface
containing light colored portions, comprising coating at least the
light color portions of the surface with the precure paint of claim
1.
7. The unvulcanized coated product of claim 6.
8. A process comprising vulcanizing the coated unvulcanized product
of claim 7.
9. The vulcanized product of claim 8.
10. The paint according to claim 1, wherein the polymer is in latex
form and the vehicle is water.
Description
This invention relates to transparent pre-cure paints and objects
coated therewith.
Pre-cure paints are well known in the art (for example, see U.S.
Pat. No. 3,595,950). They serve to form a coating on the
unvulcanized surface of a product such as a pneumatic vehicle tire
to act as a mold release and to permit flow of rubber at the
surface of the product during vulcanization so as to avoid pock
mark formation on the surface of the product. Conventionally, such
paints contain large amounts of carbon black (up to 800 parts by
weight). Normally, such paints have a non-aqueous solvent base.
Their use has been limited to dark stocks where the carbon black
would have no adverse effect on color.
There is a need for a pre-cure paint which can be used on any type
of stock, including light-colored stocks such as the white sidewall
portions of pneumatic vehicle tires, as well as the black sidewall
area adjacent thereto.
It is an object of the present invention to provide a relatively
transparent pre-cure paint which can be used on any colored stock.
Other objects will become apparent as the description proceeds.
The objects of the present invention are accomplished by the
preparation and use of a carbon black-free, pre-cure paint
containing a rubbery diene polymer, a loading amount of hydrated
amorphous silica and a zinc activation system in a solubilizable
form. The paint may have either an aqueous or non-aqueous base (see
U.S. Pat. No. 3,595,950). Any rubbery diene polymer can be used,
since all such polymers, when used as thin films, have a high
degree of transparency. Such rubbery polymers include copolymers of
butadiene and styrene, copolymers of butadiene and acrylonitrile,
polybutadiene, polyisoprene and natural rubber.
Since it is preferred that the pre-cure paints be capable of sulfur
vulcanization, it is often necessary or desirable that zinc oxide
be used as part of the vulcanization system. However, the presence
of zinc oxide in large amounts can result in a cloudy gray pre-cure
paint film. This gray color does not cause problems when used to
coat white or gray areas of a product but can cause discoloration
problems when applied to darker areas adjacent to such lighter
areas, for example, the black sidewall area of a pneumatic vehicle
tire adjacent to the white sidewall area. It is impractical to
paint the light-colored area of the tire with one type of pre-cure
paint and the adjacent black area with another pre-cure paint. It
is also often impractical to lower the amount of zinc oxide or to
replace it or to reduce the thickness of the pre-cure paint
coating.
The present invention solves the discoloration problem by using
zinc in a solubilizable form. This is accomplished by forming a
salt or complex of the zinc which is partially or totally soluble
in the diene rubber. Another embodiment involves the use of waxes
or oils. These waxes or oils can be mixed with the paint or merely
applied to the surface of the product prior to or subsequent to the
application of the paint. They aid in further solubilizing the zinc
salt or complex.
Where a water base paint is used, a polymer latex is compounded
with hydrated amorphous silica and either the solubilized form of
the zinc or zinc oxide and a compound capable of solubilizing the
zinc.
To illustrate, any of the following compounds can be used to at
least partially solubilize the zinc.
Ammonium sulfate
Tetra sodium salt of ethylene diamine tetra acetic acid
Triethylene tetra amine
Tetraethylene pentamine
Sodium gluconate
Sodium citrate
All of the above compounds were used with zinc oxide to form a
solubilized zinc activation system. All were merely added to the
polymer latex containing the zinc oxide. The hydrated amorphous
silica loaded pre-cure paint formed therefrom was used to paint an
unvulcanized product before vulcanization. After vulcanization,
each paint film possessed a greater degree of transparency than a
film formed using zinc in the non-solubilized form of zinc oxide.
The zinc oxide and the solubilizing agent, which is normally a
complexing agent, can be combined to form a complex before the
addition of either to the latex, or alternatively, can be combined
in the latex to react in situ therein to form the complex. If the
nature of the complex formation be such, the reaction between the
zinc oxide and the solubilizing agent can occur in situ in the
diene rubber.
Stearic acid is an example of a solubilizing agent capable of
forming a soluble zinc salt (zinc stearate) from the zinc
oxide.
None of the solubilized forms of the zinc need to be totally
soluble in the polymer. It is only necessary that they be more
soluble than the zinc in oxide form. Any degree of solubility will
enhance the transparency.
It is extremely important that the film be very thin in order to
maintain reasonable transparency. This thickness will naturally
vary with the amount of hydrated amorphous silica, and the presence
and levels of other ingredients within the pre-cure paint film
which would tend to reduce or increase transparency.
It is preferred that a surfactant be added to the latex to improve
the wettability of the product surface to prevent "beading up" of
the paint on the surface of the painted product. It is also
desirable that the pH of the latex be kept on the basic side (for
example, 9 to 11) with materials such as sodium carbonate to
maintain latex stability. Use of a thickener is also advantageous
in that it prevents the paint from running on the surface of the
product and also helps to prevent the latex additives from settling
out.
A typical, but not limiting, paint recipe is shown below.
______________________________________ Ingredients Parts by Weight
______________________________________ High styrene SBR latex (30%
solids) 300 Zinc oxide dispersion (50% active) 6 Antioxidant
emulsion (50% active) 2 Surfactant 1 Wetting agent (25% aqueous
solution) 2.1 pH stabilizer 6.5 Ammonium sulfate 10 Viscosity
thickener 1.6 Lubricating oil 4 Hydrated amorphous silica 80 Water
975 ______________________________________
The above paint can be used as a pre-cure paint for a white
sidewall tire without undue discoloration of the white sidewall
area or the black area adjacent thereto.
Any of the standard methods of mixing and applying the paint may be
used with the precaution that the hydrated amorphous silica and
zinc oxide preferably be ground finely.
A solvent base paint is prepared merely by dissolving a diene
polymer in the solvent and adding the ingredients according to
standard pre-cure paint techniques.
The hydrated amorphous silica is preferably used in an amount of
from 40 to 100 parts per 100 parts by weight of polymer, preferably
60 to 90 parts.
The solubilized zinc is used in an amount sufficient to provide the
same amount of zinc provided by 0.5 to 5.0 parts by weight of zinc
oxide, preferably 2 to 4 parts.
The solids of the paint can vary, but preferably is from 5 to 15
weight percent where a non-aqueous solvent is used and 10 to 20
percent where water is used.
While certain representative embodiments and details have been
shown for the purpose of illustrating the invention, it will be
apparent to those skilled in the art that various changes and
modifications may be made therein without departing from the spirit
or scope of the invention.
* * * * *